A semiconductor light emitting device is known which comprises a metallic support plate, a semiconductor light emitting element secured on the support plate, wiring conductors disposed adjacent to a top or side surfaces of the support plate to extend away from the support plate and a plastic encapsulant for sealing side surfaces of the support plate and wiring conductors. Each one end of the wiring conductors is electrically connected to a top electrode of the semiconductor light emitting element and each the other end of the wiring conductors is led out of the plastic encapsulant.
Recently, attempts have been made to apply the semiconductor light emitting devices of this kind to a light source of tail lamps or the like for automobiles, and in such a case, the light emitting devices have to light up at such an intensified emission level as to be able to positively observe lighting up or out of the devices from a distance. To this end, a semiconductor light emitting device of high optical output has been developed which can produce a light of high brightness when relatively large electric current of for example more than 350 mA is supplied through the semiconductor light emitting element as a result of study on materials and structures of the element. However, when a large electric current over 350 mA is delivered to the light emitting element, it produces an increased amount of heat during operation so that surfaces of semiconductor light emitting element may exceed a temperature of 150° C. Prior art semiconductor light emitting devices cannot produce light of high brightness because it cannot efficiently radiate heat generated from the light emitting element.
By way of example, U.S. Patent Publication 2005/0236638 to Kohji Tsukagoshi published Oct. 27, 2005 discloses a semiconductor light emitting device which comprises a support plate and a plastic encapsulant for sealing the support plate. The plastic encapsulant is formed with notches on opposite sides of the plastic encapsulant and on a bottom side of the support plate to lead each outer end of wiring conductors out of the plastic encapsulant through the notches so that exposed length of wiring conductors can be extended to the outside of the plastic encapsulant by these notches to discharge more amount of heat from the semiconductor light emitting element through the wiring conductors.
Even with the improved radiation of heat from the semiconductor light emitting element from the other end of wiring conductors, the device still cannot sufficiently release heat from semiconductor light emitting element to the outside of plastic encapsulant.
Therefore, an object of the present invention is to provide a semiconductor light emitting device capable of dissipating a full amount of heat from a semiconductor light emitting element through wiring conductors when the light emitting element is turned on with a large current flowing through the light emitting element.